The present invention relates generally to a method of improving the degree of cure for a primary coating applied onto a fiber core and optical fibers prepared according to the method.
A typical geometry for an optical fiber is characterized by a cylindrical core at the center of the fiber, a cylindrical clad surrounding the core (with the core and clad together forming the glass fiber), a primary or inner coating which surrounds the clad, and a secondary or outer coating which surrounds the primary coating. The primary coating is applied directly to the glass fiber and, when cured, forms a soft, elastic, and compliant material which encapsulates the glass fiber. The primary coating serves as a buffer to cushion and protect the glass fiber when the fiber is bent, cabled, or spooled. The secondary coating is applied over the primary coating and functions as a tough, protective outer layer that prevents damage to the glass fiber during processing and use.
One approach for preparing optical fibers utilizes a dual-coating system, whereby the primary coating material is applied to a glass fiber and the primary coating is cured, and then a secondary coating material is applied to the primary-coated fiber and the secondary coating is cured. This process is known as a wet-on-dry coating procedure. An alternate approach for preparing optical fibers also utilizes a dual-coating system, but instead the primary coating material is applied to a glass fiber followed by application of the secondary coating material and then curing of both the primary and second coatings simultaneously. This process is known as a wet-on-wet coating procedure. Both wet-on-dry and wet-on-wet coating procedures currently are rate-limited by the degree of cure for the primary coating. For the wet-on-dry process, the primary-coated fiber cannot be handled or further coated until the primary coating has sufficiently cured. Even so, because of the low cure for the primary coating, it has a lower effective modulus and is prone to defects. Similarly, even for the wet-on-wet process, further handling and processing of the coated optical fiber cannot occur until the primary coating has sufficiently cured. These too are prone to defects.
Thus, it would be desirable (i.e., cost-effective) to utilize primary coating compositions which achieve a higher degree of cure more quickly, thereby allowing for an increase in the processing speed of fiber production along with a reduction in the number and/or severity of fiber defects caused by handling and processing of optical fibers.
The present invention is directed to overcoming the above-described deficiencies in the art.
A first aspect of the present invention relates to an optical fiber including: a fiber including at least a core; a primary coating substantially encapsulating the fiber, the primary coating being the cured product of a first polymerizable composition including a first photoinitiator which absorbs light within a range of the UV spectrum; and a secondary coating substantially encapsulating the primary coating on the fiber, the secondary coating being the cured product of a second polymerizable composition including a second photoinitiator which also absorbs light within the range of the UV spectrum, wherein an average integrated intensity for the second photoinitiator is 95% or less of the average integrated intensity for the primary photoinitiator over at least a portion of the range of the UV spectrum.
A second aspect of the present invention relates to a method of making an optical fiber which includes: first coating a fiber with a first polymerizable composition including a first photoinitiator which absorbs light within a range of the UV spectrum; second coating the coated fiber with a second polymerizable composition including a second photoinitiator which also absorbs light within the range of the UV spectrum, wherein an average integrated intensity for the second photoinitiator is 95% or less of the average integrated intensity for the primary photoinitiator over at least a portion of the range of the UV spectrum; and exposing the twice coated fiber to a UV light source under conditions effective to promote curing of the first and second polymerizable compositions, thereby forming an optical fiber.
A third aspect of the present invention relates to an optical fiber made in accordance with any method of making an optical fiber as recited in this application.
A fourth aspect of the present invention relates to a method of increasing the degree of cure for a primary coating on an optical fiber. This method includes: coating an optical fiber with first and second polymerizable compositions, the first polymerizable composition including a first photoinitiator which absorbs light within a range of the UV spectrum and the second polymerizable composition including a second photoinitiator which absorbs light within the range of the UV spectrum, wherein an average integrated intensity for the second photoinitiator is 95% or less of the average integrated intensity for the primary photoinitiator over at least a portion of the range of the UV spectrum; and exposing the twice coated optical fiber to a UV light source under conditions effective to promote curing of the first and second polymerizable compositions, wherein the differential integrated intensity for the first and second photoinitiators increases the exposure of the first polymerizable composition to UV light, thereby increasing the degree of cure for the primary coating.
A fifth aspect of the present invention relates to an optical fiber ribbon or bundle which includes a plurality of substantially aligned optical fibers of the present invention and a matrix encapsulating the plurality of optical fibers.
A number of benefits are realized in connection the with products and methods of the present invention. First, by increasing the primary degree of cure for primary coating compositions, the cure speed of the primary coating is also increased by a comparative amount. As demonstrated herein, an approximately 10 percent increase in the primary degree of cure consequently resulted in an approximately 10 percent increase in the cure speed for the primary coating. This increase in cure speed can effectively be translated into higher processing speeds, enabling the production of larger quantities of optical fiber. Second, the resulting optical fiber is qualitatively enhanced by virtue of its increased degree of cure. This results in an optical fiber that can better tolerate handling (i.e., spooling and de-spooling), particularly before aging of the optical fiber, with reduced risk for causing fiber defects.